In a lithium-sulfur cell, the reduction of sulfur to lithium sulfide is a critical series of reactions that provide a large theoretical capacity of 1672 mAh/g sulfur. One of many challenges in this system is the solubility of generated lithium polysulfides during the charge/discharge process. These polysulfides derived from the reduction of elemental sulfur are soluble in organic electrolytes and can be undesirably reduced at the anode. Polysulfide species can also accumulate at the surface of the cathode and be further reduced to lower order polysulfides, such as Li2S2 or Li2S. The insulating nature of these lower order polysulfides block the electron pathway on the carbon cathode.
There is a need in the art to control the various effects of the polysulfide anion species in the lithium-sulfur system. One method is by changing the solubility properties of the electrolyte system.